improve an request against OSM Overpass API with PHP SimpleXML

The following is a little OSM Overpass API example with PHP SimpleXML I've compiled because we do not have it here for PHP and I love OSM, so let's show some useful examples.

The first part shows how tro query an Overpass Endpoint with standard PHP.
For you the second part is more interesting. That is querying the XML data; This is most easily done with xpath, the used PHP XML library is based on libxml which supports XPath 1.0 which covers the various querying needs very well.